org.sandev.basics.util
Class ReaderWriterLock

java.lang.Object
  org.sandev.basics.util.ReaderWriterLock

public class ReaderWriterLock
extends java.lang.Object

A multiple reader single writer lock utility.

Field Summary

protected int	activeReaders The number of current readers.
protected int	activeWriters The number of current writers.
protected int	waitingReaders The number of waiting readers.
protected java.util.List	writerLocks Our list of waiting writers.

Constructor Summary

ReaderWriterLock()

Method Summary

protected void	notifyReaders() Notify waiting reader threads.
protected void	notifyWriters() Release the next queued writer.
void	readCompleted() Relinquish a read lock.
void	requestRead() Request a read lock and block until it happens.
void	requestWrite() Request the write lock and block until it happens.
void	writeCompleted() Relinquish the write lock.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

activeReaders

protected int activeReaders

The number of current readers.

waitingReaders

protected int waitingReaders

The number of waiting readers. These are waiting because there is a write in progress.

activeWriters

protected int activeWriters

The number of current writers.

writerLocks

protected final java.util.List writerLocks

Our list of waiting writers. These go one at a time in the order they were registered. The list length is the number of waiting writers.

Constructor Detail

ReaderWriterLock

public ReaderWriterLock()

Method Detail

requestRead

public void requestRead()

Request a read lock and block until it happens. Caller must finally call readCompleted so the counts don't get out of whack.

readCompleted

public void readCompleted()

Relinquish a read lock. Caller must have previously acquired a lock through requestRead or the counts will get out of whack.

requestWrite

public void requestWrite()

Request the write lock and block until it happens. Caller must finally call writeCompleted so the counts don't get out of whack.

writeCompleted

public void writeCompleted()

Relinquish the write lock. Caller must have previously acquired a lock through requestWrite or the counts will get out of whack.

notifyReaders

protected void notifyReaders()

Notify waiting reader threads. Must be called from within a synchronized method.

notifyWriters

protected void notifyWriters()

Release the next queued writer. Must be called from within a synchronized method.